lkml.org 
[lkml]   [2020]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v2 5/7] mm: parallelize deferred_init_memmap()
    Date
    Deferred struct page init is a significant bottleneck in kernel boot.
    Optimizing it maximizes availability for large-memory systems and allows
    spinning up short-lived VMs as needed without having to leave them
    running. It also benefits bare metal machines hosting VMs that are
    sensitive to downtime. In projects such as VMM Fast Restart[1], where
    guest state is preserved across kexec reboot, it helps prevent
    application and network timeouts in the guests.

    Multithread to take full advantage of system memory bandwidth.

    The maximum number of threads is capped at the number of CPUs on the
    node because speedups always improve with additional threads on every
    system tested, and at this phase of boot, the system is otherwise idle
    and waiting on page init to finish.

    Helper threads operate on section-aligned ranges to both avoid false
    sharing when setting the pageblock's migrate type and to avoid accessing
    uninitialized buddy pages, though max order alignment is enough for the
    latter.

    The minimum chunk size is also a section. There was benefit to using
    multiple threads even on relatively small memory (1G) systems, and this
    is the smallest size that the alignment allows.

    The time (milliseconds) is the slowest node to initialize since boot
    blocks until all nodes finish. intel_pstate is loaded in active mode
    without hwp and with turbo enabled, and intel_idle is active as well.

    Intel(R) Xeon(R) Platinum 8167M CPU @ 2.00GHz (Skylake, bare metal)
    2 nodes * 26 cores * 2 threads = 104 CPUs
    384G/node = 768G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 4078.0 ( 9.0) -- 1779.0 ( 8.7)
    2% ( 1) 1.4% 4021.3 ( 2.9) 3.4% 1717.7 ( 7.8)
    12% ( 6) 35.1% 2644.7 ( 35.3) 80.8% 341.0 ( 35.5)
    25% ( 13) 38.7% 2498.0 ( 34.2) 89.1% 193.3 ( 32.3)
    37% ( 19) 39.1% 2482.0 ( 25.2) 90.1% 175.3 ( 31.7)
    50% ( 26) 38.8% 2495.0 ( 8.7) 89.1% 193.7 ( 3.5)
    75% ( 39) 39.2% 2478.0 ( 21.0) 90.3% 172.7 ( 26.7)
    100% ( 52) 40.0% 2448.0 ( 2.0) 91.9% 143.3 ( 1.5)

    Intel(R) Xeon(R) CPU E5-2699C v4 @ 2.20GHz (Broadwell, bare metal)
    1 node * 16 cores * 2 threads = 32 CPUs
    192G/node = 192G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 1996.0 ( 18.0) -- 1104.3 ( 6.7)
    3% ( 1) 1.4% 1968.0 ( 3.0) 2.7% 1074.7 ( 9.0)
    12% ( 4) 40.1% 1196.0 ( 22.7) 72.4% 305.3 ( 16.8)
    25% ( 8) 47.4% 1049.3 ( 17.2) 84.2% 174.0 ( 10.6)
    37% ( 12) 48.3% 1032.0 ( 14.9) 86.8% 145.3 ( 2.5)
    50% ( 16) 48.9% 1020.3 ( 2.5) 88.0% 133.0 ( 1.7)
    75% ( 24) 49.1% 1016.3 ( 8.1) 88.4% 128.0 ( 1.7)
    100% ( 32) 49.4% 1009.0 ( 8.5) 88.6% 126.3 ( 0.6)

    Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, bare metal)
    2 nodes * 18 cores * 2 threads = 72 CPUs
    128G/node = 256G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 1682.7 ( 6.7) -- 630.0 ( 4.6)
    3% ( 1) 0.4% 1676.0 ( 2.0) 0.7% 625.3 ( 3.2)
    12% ( 4) 25.8% 1249.0 ( 1.0) 68.2% 200.3 ( 1.2)
    25% ( 9) 30.0% 1178.0 ( 5.2) 79.7% 128.0 ( 3.5)
    37% ( 13) 30.6% 1167.7 ( 3.1) 81.3% 117.7 ( 1.2)
    50% ( 18) 30.6% 1167.3 ( 2.3) 81.4% 117.0 ( 1.0)
    75% ( 27) 31.0% 1161.3 ( 4.6) 82.5% 110.0 ( 6.9)
    100% ( 36) 32.1% 1142.0 ( 3.6) 85.7% 90.0 ( 1.0)

    AMD EPYC 7551 32-Core Processor (Zen, kvm guest)
    1 node * 8 cores * 2 threads = 16 CPUs
    64G/node = 64G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 1003.7 ( 16.6) -- 243.3 ( 8.1)
    6% ( 1) 1.4% 990.0 ( 4.6) 1.2% 240.3 ( 1.5)
    12% ( 2) 11.4% 889.3 ( 16.7) 44.5% 135.0 ( 3.0)
    25% ( 4) 16.8% 835.3 ( 9.0) 65.8% 83.3 ( 2.5)
    37% ( 6) 18.6% 816.7 ( 17.6) 70.4% 72.0 ( 1.0)
    50% ( 8) 18.2% 821.0 ( 5.0) 70.7% 71.3 ( 1.2)
    75% ( 12) 19.0% 813.3 ( 5.0) 71.8% 68.7 ( 2.1)
    100% ( 16) 19.8% 805.3 ( 10.8) 76.4% 57.3 ( 15.9)

    Server-oriented distros that enable deferred page init sometimes run in
    small VMs, and they still benefit even though the fraction of boot time
    saved is smaller:

    AMD EPYC 7551 32-Core Processor (Zen, kvm guest)
    1 node * 2 cores * 2 threads = 4 CPUs
    16G/node = 16G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 722.3 ( 9.5) -- 50.7 ( 0.6)
    25% ( 1) -3.3% 746.3 ( 4.7) -2.0% 51.7 ( 1.2)
    50% ( 2) 0.2% 721.0 ( 11.3) 29.6% 35.7 ( 4.9)
    75% ( 3) -0.3% 724.3 ( 11.2) 48.7% 26.0 ( 0.0)
    100% ( 4) 3.0% 700.3 ( 13.6) 55.9% 22.3 ( 0.6)

    Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz (Haswell, kvm guest)
    1 node * 2 cores * 2 threads = 4 CPUs
    14G/node = 14G memory

    kernel boot deferred init
    ------------------------ ------------------------
    node% (thr) speedup time_ms (stdev) speedup time_ms (stdev)
    ( 0) -- 673.0 ( 6.9) -- 57.0 ( 1.0)
    25% ( 1) -0.6% 677.3 ( 19.8) 1.8% 56.0 ( 1.0)
    50% ( 2) 3.4% 650.0 ( 3.6) 36.8% 36.0 ( 5.2)
    75% ( 3) 4.2% 644.7 ( 7.6) 56.1% 25.0 ( 1.0)
    100% ( 4) 5.3% 637.0 ( 5.6) 63.2% 21.0 ( 0.0)

    On Josh's 96-CPU and 192G memory system:

    Without this patch series:
    [ 0.487132] node 0 initialised, 23398907 pages in 292ms
    [ 0.499132] node 1 initialised, 24189223 pages in 304ms
    ...
    [ 0.629376] Run /sbin/init as init process

    With this patch series:
    [ 0.227868] node 0 initialised, 23398907 pages in 28ms
    [ 0.230019] node 1 initialised, 24189223 pages in 28ms
    ...
    [ 0.361069] Run /sbin/init as init process

    [1] https://static.sched.com/hosted_files/kvmforum2019/66/VMM-fast-restart_kvmforum2019.pdf

    Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
    ---
    mm/Kconfig | 6 ++---
    mm/page_alloc.c | 60 ++++++++++++++++++++++++++++++++++++++++++++-----
    2 files changed, 58 insertions(+), 8 deletions(-)

    diff --git a/mm/Kconfig b/mm/Kconfig
    index c1acc34c1c358..04c1da3f9f44c 100644
    --- a/mm/Kconfig
    +++ b/mm/Kconfig
    @@ -750,13 +750,13 @@ config DEFERRED_STRUCT_PAGE_INIT
    depends on SPARSEMEM
    depends on !NEED_PER_CPU_KM
    depends on 64BIT
    + select PADATA
    help
    Ordinarily all struct pages are initialised during early boot in a
    single thread. On very large machines this can take a considerable
    amount of time. If this option is set, large machines will bring up
    - a subset of memmap at boot and then initialise the rest in parallel
    - by starting one-off "pgdatinitX" kernel thread for each node X. This
    - has a potential performance impact on processes running early in the
    + a subset of memmap at boot and then initialise the rest in parallel.
    + This has a potential performance impact on tasks running early in the
    lifetime of the system until these kthreads finish the
    initialisation.

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index d0c0d9364aa6d..9cb780e8dec78 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -68,6 +68,7 @@
    #include <linux/lockdep.h>
    #include <linux/nmi.h>
    #include <linux/psi.h>
    +#include <linux/padata.h>

    #include <asm/sections.h>
    #include <asm/tlbflush.h>
    @@ -1814,16 +1815,44 @@ deferred_init_maxorder(u64 *i, struct zone *zone, unsigned long *start_pfn,
    return nr_pages;
    }

    +struct definit_args {
    + struct zone *zone;
    + atomic_long_t nr_pages;
    +};
    +
    +static void __init
    +deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
    + void *arg)
    +{
    + unsigned long spfn, epfn, nr_pages = 0;
    + struct definit_args *args = arg;
    + struct zone *zone = args->zone;
    + u64 i;
    +
    + deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn, start_pfn);
    +
    + /*
    + * Initialize and free pages in MAX_ORDER sized increments so that we
    + * can avoid introducing any issues with the buddy allocator.
    + */
    + while (spfn < end_pfn) {
    + nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
    + cond_resched();
    + }
    +
    + atomic_long_add(nr_pages, &args->nr_pages);
    +}
    +
    /* Initialise remaining memory on a node */
    static int __init deferred_init_memmap(void *data)
    {
    pg_data_t *pgdat = data;
    const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
    unsigned long spfn = 0, epfn = 0, nr_pages = 0;
    - unsigned long first_init_pfn, flags;
    + unsigned long first_init_pfn, flags, epfn_align;
    unsigned long start = jiffies;
    struct zone *zone;
    - int zid;
    + int zid, max_threads;
    u64 i;

    /* Bind memory initialisation thread to a local node if possible */
    @@ -1863,11 +1892,32 @@ static int __init deferred_init_memmap(void *data)
    goto zone_empty;

    /*
    - * Initialize and free pages in MAX_ORDER sized increments so
    - * that we can avoid introducing any issues with the buddy
    - * allocator.
    + * More CPUs always led to greater speedups on tested systems, up to
    + * all the nodes' CPUs. Use all since the system is otherwise idle now.
    */
    + max_threads = max(cpumask_weight(cpumask), 1u);
    +
    while (spfn < epfn) {
    + epfn_align = ALIGN_DOWN(epfn, PAGES_PER_SECTION);
    +
    + if (IS_ALIGNED(spfn, PAGES_PER_SECTION) &&
    + epfn_align - spfn >= PAGES_PER_SECTION) {
    + struct definit_args arg = { zone, ATOMIC_LONG_INIT(0) };
    + struct padata_mt_job job = {
    + .thread_fn = deferred_init_memmap_chunk,
    + .fn_arg = &arg,
    + .start = spfn,
    + .size = epfn_align - spfn,
    + .align = PAGES_PER_SECTION,
    + .min_chunk = PAGES_PER_SECTION,
    + .max_threads = max_threads,
    + };
    +
    + padata_do_multithreaded(&job);
    + nr_pages += atomic_long_read(&arg.nr_pages);
    + spfn = epfn_align;
    + }
    +
    nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
    cond_resched();
    }
    --
    2.26.2
    \
     
     \ /
      Last update: 2020-05-20 20:28    [W:5.253 / U:0.060 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site